I have created azure devops with a few organizations/projects in it. Do I need to scale or replicate it across different datacenters so all the developers across the globe can access it? Any references appreciated.
Manual intervention is not required for your Azure Devops organisation to be accessible to different developers accross the globe.
The on-premises version of Azure Devops can be scaled with multi-server deployments. However it's common to only deploy these servers to a single datacenter.
Azure DevOps is already replicated across multiple Azure Data Centers. They did this after the south east data center hosting Azure Devops (then VSTS) went down for a few days, bringing down the service. By going with a cloud provider, this is one of the benefits you (assume) you get. Automatic (geo)replication/redundancy of SAAS products. You don't have to manage this, but if something goes wrong, you have no control (or responsibility) to fix it.